1. Field of the Invention
The present invention relates to an optical substrate such as a cover glass for displays which is used for a touch panel. More particularly, the present invention is concerned with an optical substrate that has, for example, a reinforcement layer, which is intended to prevent cracking, formed on a glass substrate, has an antiglare layer such as a microstructure formed on the reinforcement layer, has a tone-adjustment antireflection film formed on the antiglare layer, and has an antifouling layer, which is intended to minimize fingerprint adhesion, formed on the antireflection film.
2. Description of Related Art
In the past, a filter with an antireflection feature for display devices which has a reinforcement layer formed by performing reinforcement treatment on a glass substrate, and has a tone-adjustment antireflection film formed on the reinforcement layer has been known.
For example, in Japanese Patent No. 4078520, as described especially in paragraphs 0039 to 0045, an oxynitride tin film of 107 nm thick is formed as a first layer directly on a glass substrate, and a silicon dioxide film of 72 nm thick is further formed as a second layer in order to thus perform reinforcement treatment on the glass. A PET-coated reflective film that has undergone tone correction is bonded to the conductive film with an acrylic adhesive between them, whereby an antireflection filter is fabricated.
In Japanese Patent No. 3710721, as described in paragraphs 0063 to 0065 and shown in FIG. 2, a functional film (C) 40 is formed on a conductive mesh layer (B) 10 with a pigment-containing translucent adhesive (D) 30 between them. The functional film (C) 40 has a near-infrared absorbent containing layer 41, a polymer film 43, and an antireflection layer 42, which is hard-coated and has antistatic and antifouling properties, stacked in that order.
Further, paragraph 0032 of Japanese Patent No. 3710721 discloses the functional translucent layer (c) preferably has any of the features of an antireflection (AR) property for suppressing outside light reflection, an antiglare (AG) property for preventing projection of a mirror image, and an antireflection and antiglare (ARAG) property including both the properties.
An existing filter with an antireflection feature cannot be employed in portable electronic equipment or portable telecommunications equipment (for example, a portable cellular phone such as a smartphone or a mobile device such as an iPad (registered trademark)) as it is. This is because since the equipment is of a portable type, the equipment receives a larger amount of incident light, which comes from outside, than electric and electronic equipment such as a television set or personal computer does. Therefore, a change in a reflected color dependent on the incident light is very large and a transmittance is insufficient.
As an antifouling film, a water-repellent and oil-repellent film is well known. For the aforesaid usage, the antifouling film has to exhibit high abrasion durability. In addition, since the antifouling film is always dustproof, measures have to be taken against dustproofness. Further, the antifouling film has to be so thin as not to affect the optical characteristics of an antireflection film. However, the antifouling film capable of satisfying these requirements simultaneously is unavailable.